Alternating-current generator.



PATENTED DEC. 25, 1906. E. F. W. ALEXANDERSON.

ALTERNATING CURRENT GENERATOR.

APPLICATION FILED KAY 5, 1905.

Fig.2. Fig.3.

- Fig.4 Fig.5,

i gwm Fig.6. z d 3 5 EmstF.w;I e:::;erson MW T W ERNST F. W. ALEXANDERSON, OF SCHENE a rectifying-commutator and with an auxilarranged has essentially the characteristics" of a s UNITED s'rA'rEs PATENT OFFICE.

O'IADY, NEW YORK, ASSIGNOR A CORPORATION OF NEW YORK.

ALTERNATING-CURRENT GENERATOR.

TO GENERAL ELECTRIC COMPANY,

Specification of Letters Patent.

' Application filed May a, 1905. Serial No. 259,066.

Patented Dec. 25, 1906.

To all whom it may concern: I mum output of the machine, while compound- Be it known that I, ERNST F. W. ALEXAN- ing in a small alternating-current generator DERSON, a subject of the King of Sweden and adds greatly to the complication and ex- Norway, residing at Schenectady, county of pense.

Schenectady, State of New York, have in- By my invention I am enabled to obtain vented certain new and useful Improvecurrents of great magnitude at exceedingly ments in Alternating-Current Generators, of I low voltages without the use of resistances which the following is a specification. in the work-circuit or compounding of any My invention relates to alternating-current kind. I accomplish this result by dividing generators; and its object is to provide a the armature-windingintoaplurality of relasimple and efiicient self-exciting alternatingtively displaced sections, all or a portion of current generator capable of operating over whichmay be connected in varying relations Wide ranges both of current and of voltage. to the work-circuit. With a machine thus One kind of work to which a generator ararranged ordinary variations in the current mnged in accordance with my invention is and voltage desired maybe obtained by conespecially applicable is for thawing waternecting the armature-sections in diil'erent pipes. For such a purpose an alternatingrelations to the work-circuit, supplementing current generator is better suited than a dithese variations by manipulation of the fieldrect-current generator, not only because of rheostat. When currents of large amount the comparative absence of electrolytic efand low fects, but also because it is verydiflicult to of a short pipe of large diameter, I cut out of design a direct-current generator which will circuit the sections of the armature-winding operate sparklessly over wide ranges of curon part of the armature. A portion of the rent and voltage. If an alternating-current armature is thus rendered idle, as far as supgenerator is used, it is extremely desirable plying the work-circuit is concerned, and that it should be self-exciting, for with small consequently the armature reaction, which machines, such as would be used for this by weakening the field is the cause of the loss class of work, a separate exciter would add of excitation in machines as ordinarily argreatly to the cost. It has been proposed ranged, is substantially eliminated at the eretofore to make alternating-current genidle portions of the armature, which portions erators self-exciting by providing them with. may be employed for generating the exciting voltage. Consequently substantially full voltage is induced in the auxiliary excitingwinding at the idle portions regardless of the load upon the armature, so that the machine maintains its excitation.

iary exciting-winding:carried by the armature and connected to the field-winding through. the commutator, A generator so unt-machine, and, as is well known, a shunt-generator will not maintain its voltage if the resistance of the work-circuit is lowered beyond certain limits. In such work as thawing water-pipes it will sometimes happen that the resistance in the work-circuit is exceedingly low, since a short pipe of large diameter acts almost as a short circuit upon the machine. Consequently self-exci ting generators of the type mentioned above, as ordinarily arranged, would lose their excitation and could not be used for the purpose in view unless resistances were placed in the work-circuit or some compounding means were employed. The use of resistances would greatly reduce the efficiency and maxiin placing the exciting- Winding only at that portion of the armature that is idle on very heavy loads, so that the maximum effect of the exciting-windin is at all times obtained.

In order to avoid a lateral strain on the shaft, which would occur if the portions of the armature-winding cut out of circuit were not symmetrically positioned, I so arrange the armature-sections and their terminal connections that diametrically opposite armature-sections may be cut out of circuit.

By invention will best be understood by reference to the accompanying drawings, in which- Figure 1 shows diagrammatically a selfvoltage are required, as in the case Another feature of my invention consists 5 exciting a'lternatingcurrent generator ar Grannne ring. The armature-wimling is di vided into four sections A, A'-,- A, and A which are relativelydisplaced around the armature. From each section leads are brought out to a terminal board. Thus the section A is connected to the terminalst, section A to terminals t'-, &c. F represents the field l l l i l l structure provided with the usual field-coils (indicated byf) and also provided with a rectiiying commutator C and comnnitatorbrushes '1). The arrangement of commutator and brushes which is shown in the drawings is that which I have fully described in a former patent, No. 789,476, issued to me May it, IDOSzbut .tofacilitate the understanding of my present invention 1 shall brielly describe the arrangement here. The brushes bare given what I may term a polyphase arrangementon the commutator. The particular arrangement shown is threephase, comprising three brushesdisplaced from each other by onehundred and twenty electricaldegrees. I Eachot'the(mmmutatorsegments is substantially equal in length to the distance between brushes, so that at the instant a segment is leaving one brush it makes contact with another brush. The machinoshown in the drawings being a four-pole generator, four connnutator-segments are employed,. opposite segments. being crossconnecte'd; y

.The brushes I) areisupplied from athreephase auxiliary. exciting-winding carried by the armature. The phases of this winding areindicated by reference-letters a ai and (1 respectively. Each phase, as shown, consistsof two ooils'arranged diametrically opposite each other. One terminal of each phase is connected to a brush, and the other terminals are connected to each other in star or Y connection through the three-arm rheostatR, by means of which the held excitation may be varied. The three arms of the rheostat are adapted to cut varying portions of resistances 7 into series with the auxiliary ex- In the position shown all resistance is cutout of clrcuit except the rc- CItlIlg-NVllldlIlg.

sistances 1', which may belett permanently the flow of short-circuit current when. two

commutator-brushesare momentarily short circuited by a commutator-segment. The. brushes are so arranged, as disclosed in my former application, that this shortcircuiting occurs at the moment when the voltages in the two phases short-circuited are approximately equal, so that no short-circuit current of any appreciable amount can flow. If the duced in the usual manner.

rheost-at is moved in a clockwise direction, viewed in Fig. 1,.the resistances '1' will be cut into circuit with the auxiliary exciting-windingand the excitation will be gradually re lt' this n1ovement is continued beyond the last contact ol' the resistances r, thehigh resistances r are thrown into the lieldcircuit, thereby increasing the resistance in the field-circuit above the criticalamount, so that the machine loses its excitation entirely. \Vith this arrangementno field-switch is required, since the machine may be excited and put out of service by the rheostat-handle, and the arcing that occurs when a h ld-circuit is broken is wholly avoided.

\Vith the arrangement as described above it is obvious that a considerable range ol" cur rent and voltage may be obtained by varying the connect ons of the armattire-sections to the work-circuit. Thus if the terminal connections are as shown in Fig. .2 all four armatlire-sections are connected in parallel to the work-circuit. The machine-terminals are indicated at T T. if the connections are as indicated in Fig. 3, the sections A and A are connected in parallel with each, and the sections A and A are also connected in pari l l i l l l l l l l allel, the two groups being connectt-ul in series. The voltage is thus twice as great as that obtained in Fig. 2. Fig. 4 shows the connections with all the sections in series. This connection would be employed l'or long pipes of small diameter. ln the case of very short. pipes of large diameter the connection shown in Fig. 5 is employed. tion the sections A" and A are cut out of circuit, while the sections A and A are connected in parallel to the work-circuit. Thus the portions of the armature on which the excitingwinding iscarried are idle, as lar as the main armature-current. is concerned. and consequently however large the amount of current flowing in the sections A and A the auxiliary exciting-winding is ail'ected to a very small extent by the armature reaction. The machine is thus enabled to maintain its load even on a complete short circuit. .\Ioreover, it-will be seen that since the armaturesections, which are out of circuit, are diametrically opposite each other the magnetic pull of the field on the armature is balancedon all diameters, so that there is no tendency to strain the shaft. Fig. 6 shows still another connection in which the sections A and A in circuit in order to oppose any tendency to are still out of circuit, while the sections A and A are connected in series to the Workcircuit. This arrangement would be enrployed for pipes of a somewhat greater length or asom'ewhat smaller diameter than those for which the arrangement shown in Fig. 5 is suited. c

I have described my invention with a view to its application in thawing pipes, since this type of work atl'ords a good illustration of the \Yith this connec-- it will be understood that in practice any ad vantages my invention ol'l'ers; but it will of course be understood that my invention is in no way limited to this particular application, but may be used to advantage \\-'herever alternating current. varying over wide ranges in current and voltage is required. Furthermore, while for the sake of simplicity I have illustrated my invention diagrammatically well-known type of inachine may be employed for the purposes of my invention. Consequently I do not desire to limit myself to the particular construction and arrangement of parts here shown, but aim in the appended claims to cover all modifications which are Within the scope of my invention.

What I claim as new, and desire to secure by Letters Patent of the United States, is

1. In an alternating-current generator, a field-winding provided with a rectifyingcommutator and brushes, an armature-winding arranged in sections, means for connecting said sections in varying relations to the work-circuit, and an auxiliary exciting-winding carried by the armature and connected to said brushes. 1

2. In an alternating-current generator, a field-winding provided with a rectifyingconnnutator, a polyphase arrangement of brushes bearing on said commutator, an ar mature-winding arranged in sections, means for connecting said sections in varying rela- I tions to the worlccircuit, and a poly hase auxiliary exciting-winding carried by t 1 armature and connected to said brushes.

3. In an alternating-c1irrent generator, a field-winding provided with a rectifyingcoinlnutator and brushes, an armaturewinding arranged in sections, an auxiliary exciting-winding carried by the armature and connected to said brushes, and means for cutting a portion of the sections of the armature-windings out of circuit when our rents of large volume and low voltage are required.

4. In an alternating-current generator, a field-winding provided with a rectifyingcomnnttator, a polyphase arrangement of .iieldwinding provided with a rectifying-g brushes bearing on said connnutator, an ar mature-winding arranged in sections, a polyphase auxiliary exciting-winding carried by the armature and connected to said brushes, and means for cutting a portion of the sections of the arn1aturewinding out of circuit when currents of large amount and low voltage are required.

' 5. In an alternating-current generator, a

commutator and brushes, an armat urewinding comprising a plurality of relatively displaced" sections, meansfor connecting all or a portion of said sections to the work-circuit, and an auxiliary exciting-Winding extending over only a portion of the armature and connected to said brushes.

6'. In an alternating-current generator, a field-winding provided with. a rectifyingcommutator, a polyphase arrangement of brushes bearing on said connnutator, an armature-winding comprising a plurality of relatively displaced sections, means for connecting all or a portion of said sections to the work-circuit, and a polyphase auxiliary exciting-winding extending over only a port-ion of said armature and connected to said brushes.

7. In an alternating-current generator, a field winding commutator and brushes, an armaturewinding comprising a plurality of relatively displaced sections, means for cutting a portion of said sections out of circuit and con necting the remaining sections to the workcircuit, and an auxiliary exciting-winding carried by the idle portion of the armature and connected to said brushes.

In an alternating-current generator, a field-winding provided with a rectifyingcommut-ator, a polyphase arrangementof brushes bearing on said commutator, an armature-winding comprising a plurality of relatively displaced sections, means for cutting a portion of said sections out ofcircuit' and connecting the remaining sections to the work-circuit, and a polyphase auxiliary exciting-winding carried by the idle portion of the armature and connected to said brushes.

9. In an alternatingcurrent generator, a held-Winding provided with a rectifyingcommuta-tor and brushes, an armaturewinding comprising a plurality of relatively displaced sections, means for cutting diametrically opposite sections out of circuit and connecting the remaining sections to the work-circuit, and an auxiliary excitingwinding carried by the idle portion of the arn'iature and connected to said brushes.

10. In an alternating-current generator, a field-winding provided with a rectifyingcommutator, a polyphase arrangement of brushes bearing on said commutator, an armature-winding comprising a plurality of relatively displaced sections, means for cutting diametrically opposite sections out of circuit and connecting the remaining sections to the work-circuit, and a polyphase auxiliary exciting-winding carried by the idle portion of the armature and connected to said brushes.

In witness whereof I have hereunto set my hand this 4th day of May, 1905.

ERNST F. W. ALEXANDERSON. 

